Since photographic light-sensitive materials are generally composed of a support having an electrically insulating property and photographic layers, static charges often accumulate during production or use of the photographic light-sensitive materials, caused by contact friction between surfaces of the light-sensitive material or with other materials, or by separation thereof. Such accumulated static charges cause various problems, the most serious of which is that the light-sensitive emulsion layer can be exposed to light by discharge of accumulated static charges prior to development. This causes dot like spots or resinous or feathery linear spots upon development processing of the photographic film. This phenomenon of static marks greatly reduces the commercial value of the photographic films or results in its complete loss. For example, it is evident that static marks could result in a dangerous misinterpretation when they appear on medical or industrial X-ray films. Since this phenomenon becomes evident for the first time after development, processing, it is very troublesome. Further, the accumulated static charges cause secondary problems, for example, causing dust to adhere to the surface of the film or preventing uniform application of photographic layers to the film.
Such static charges often accumulate when producing photographic light-sensitive materials or using them, as described above. For example, during production, they are generated by contact friction between a photographic film and a roll, or by separation of the support face and the emulsion face when winding or rewinding the photographic film. Further, they are generated in an automatic photographing apparatus by contact of an X-ray film with machine parts or by contact of an X-ray film with fluorescent sensitizing paper or the separation therefrom. In addition, they are generated by contact of film with packing materials. Static marks caused by accumulation of such static charges increase rather substantially with increases in the sensitivity of photographic light-sensitive material, and increase with a faster processing rate. Particularly in recent years, static marks have become a more serious problem, because photographic light-sensitive materials now commonly have high sensitivity and are often subjected to severe handling in high speed applications, high speed photography or high speed automatic processing.
In order to reduce the problems created by static electricity, antistatic agents are preferably added to photographic light-sensitive materials. Antistatic agents utilized in photographic light-sensitive materials must have different characteristics than antistatic agents conventionally used in other fields because of various characteristic restrictions applicable to photographic light-sensitive materials. Antistatic agents for use in photographic light-sensitive materials must not only have excellent antistatic properties but they must not adversely affect photographic properties such as sensitivity, fog, granularity of sharpness, etc. In addition, they must not reduce the film strength of the photographic light-sensitive materials (i.e., reduce resistance to scratches formed by friction or scratching), they must not diminish antiadhesive properties (i.e., permit the surface of the photographic light-sensitive material to easily adhere to another surface of the photographic light-sensitive material or other surfaces), they must not promote exhaustion of solutions used for processing the photographic light-sensitive materials, and they must not reduce the adhesive strength between layers of the photographic light-sensitive materials. Accordingly, the application of antistatic agents to photographic light-sensitive materials is subjected to a number of significant restrictions.
One method of reducing static electricity is by increasing the electrical conductivity of the surface of the photographic light-sensitive material in order to quickly discharge static charges prior to the discharge of the accumulated charges and thus prevent accumulated charges.
Various methods of increasing the electrical conductivity of the support of the photographic light-sensitive materials, and various surface coating layers are known, including the use of hygroscopic substances and water-soluble inorganic salts, certain kinds of surface active agents and polymers. For example, the use of polymers is described in U.S. Pat. Nos. 2,882,157, 2,972,535, 3,062,785, 3,262,807, 3,514,291, 3,615,531, 3,753,716 and 3,938,999, the use of surface active agents is described in U.S. Pat. Nos. 2,982,651, 3,428,456, 3,457,076, 3,454,625, 3,552,972 and 3,655,387, and the use of metal oxides and colloidal silica is described in U.S. Pat. Nos. 3,062,700, 3,245,833 and 3,525,621.
However, it is very difficult to apply these substances generally to photographic light-sensitive materials, because they are particularly suited for one kind of film support or photographic composition. Accordingly, while they produce good results when used with a specific film support, photographic emulsion, or other photographic element, they are useless for preventing static charges when used with different film supports and photographic elements. They may have excellent antistatic properties but adversely affect photographic properties such as sensitivity of photographic emulsions, fog, granularity or sharpness. They may have excellent antistatic properties immediately after production, but which deteriorate with the passage of time.
It is also very important that the photographic properties of photographic light-sensitive materials are not significantly changed depending on conditions of development processing such as development temperature or degree of exhaustion of the developing solution. Particularly, in recent years, high temperature rapid development processing has become generally used, and slight changes in the conditions of such processing tend to significantly alter the photographic properties of photographic light-sensitive materials. When the photographic properties are greatly influenced by a slight change in the conditions of development processing as described above, it is impossible to obtain images of constant quality, greatly reducing the commercial value of the photographic light-sensitive materials.
It is also known that nonionic surface active agents having one polyoxyethylene chain in a molecule described in British Pat. No. 861,134 and German Pat. No. 1,422,309 have excellent antistatic properties. Some of these nonionic surface active agents having one polyoxyethylene chain in a molecule can prevent changes in photographic properties resulting from variations in conditions of development processing as described above. However, they have serious disadvantages when they are applied to photographic light-sensitive materials. Specifically, (1) they remarkably reduce sensitivity, (2) since their antistatic properties deteriorate with the passage of time, although they have good antistatic properties immediately after production, the antistatic properties of products are inferior by the time when the products are used, (3) in particular, when used in X-ray materials, dotted or meshlike uneven density (which is called "screen contamination") results in the sensitive materials after development processing, because of their contact with sensitizing paper (i.e., a fluorescent screen) during exposure and (4) when applied to X-ray materials, dotted fog results in the materials after development processing using an automatic developing machine. It can be easily understood that the commercial value of photographic light-sensitive materials with such disadvantages is remarkably reduced.
A proposal to prevent the change of photographic properties caused by variations in conditions of development processing, by incorporating an inorganic acid salt or organic acid salt of nitron in photographic light-sensitive materials is described in Japanese Patent Application (OPI) No. 22626/75. (The term "OPI" as used herein refers to a "published unexamined Japanese patent application", hereinafter the same). Although the incorporation of an inorganic acid salt or organic acid salt of nitron can reduce the change of photographic properties due to variations in development temperature or degree exhaustion of developing solution to some extent, the effect is insufficient and it is very difficult to obtain images of constant quality by the use of these compounds alone. It is quite difficult to produce photographic light-sensitive materials having both excellent antistatic properties and excellent photographic properties which are not significantly affected by variations in development processing conditions.